The present invention relates to motor brake assemblies. More particularly, the present invention relates to motor brake assemblies incorporating a printed circuit board which simplifies the assembly of the motor brake assembly and provides for the grounding of the stators for the electromagnetic coils.
A typical brake assembly for an electric motor comprises a stationary brake housing, a brake pack and an actuating mechanism. The brake housing is a stationary housing normally bolted directly to the motor or it is bolted to the motor through an adaptor plate. The brake pack is usually positioned within the brake housing and comprises a rotating member which rotates with the drive shaft of the motor and a fixed portion which is fixedly secured to the brake housing. The brake pack further includes a plurality of driving friction discs which are secured to the rotating member and interleaved with a plurality of driven friction discs which are secured to the fixed member. The actuating mechanism selectively moves the brake pack between an applied condition where the driving and driven discs are compressed together and a released condition where the driving discs are allowed to rotate relative to the driven discs. Thus, the rotation of the shaft of the motor can be stopped or prohibited when the driving and driven friction discs are compressed together by the actuating mechanism.
The actuating mechanism normally comprises an actuating disc which is longitudinally movable within the brake housing between the applied condition and the released condition. In the applied condition, the actuating disc compresses the plurality of driving and driven friction discs between two abutment surfaces to effectively lock the drive shaft of the motor to the stationary brake housing. In the released condition, the actuating disc releases the compressive load on the plurality of driving and driven friction discs and the drive shaft of the motor is allowed to rotate relative to the stationary brake housing. The movement of the actuating disc within the stationary brake housing is typically controlled by a plurality of electromagnetic coils fixedly secured to the stationary brake housing. The electromagnetic coils magnetically attract the actuating disc which then moves longitudinally against a biasing force. The biasing force is normally provided by a plurality of springs which bias the actuating disc away from the electromagnetic coils and into an applied condition for safety reasons although it would be possible to bias the actuating disc into a released condition if desired. When power is supplied to the electromagnetic coils, the actuating disc is magnetically attracted against the biasing load to release or apply the brake depending on its position of the brake due to the biasing load.
The above described prior art motor brake assemblies have been designed to either run dry or they have been designed to be submerged in a cooling fluid operating under the oil shear principle. In simple terms, the oil shear principle is based on the use of multiple interleaved discs bathed in oil. A positive oil film is maintained between each of the disc surfaces. When the interleaved discs are compressed together, torque is transmitted by the viscous shearing of this oil film. The result is that the wear of the friction surfaces on the discs is greatly reduced. In addition, heat is dissipated by the circulating oil for fast cyclic capability.
Prior art motor brake assemblies have the electromagnetic coils circumferentially arranged in an annular recess provided in a coil housing which forms a part of the stationary brake housing. Each individual electromagnetic coil is held in place by a bolt and once located the electromagnetic coils are wired together with power being supplied to the plurality of electromagnetic coils through an access hole extending through the coil housing. In some motor brake assemblies, instead of bolting each electromagnetic coil to the coil housing, the plurality of electromagnetic coils can be wired together and be potted into the annular recess of the coil housing by a non-conductive material such as epoxy. The epoxy will entirely fill the annular recess and cover the electrical connection between the coils.
While these prior art motor brake units are effective, especially when using the oil shear principle, the assembly of the motor brake units has proven to be an especially time consuming and expensive operation. This is particularly true when considering the assembly and wiring of the plurality of electromagnetic coils into the annular recess of the coil housing. In addition, the stators for the electromagnetic coils are not grounded which can lead to the problem of sparking between the stator and a nearby grounded component. Accordingly, what is needed is a cost effective assembly method for locating and wiring the plurality of electromagnetic coils within the coil housing which forms a part of the stationary brake housing. The wiring of the plurality of electromagnetic coils should also include a system for grounding the stators of the coils.
The present invention provides the art with a simplified and cost effective method of locating and wiring the plurality of electromagnetic coils within the coil housing. The present invention utilizes an annular shaped printed circuit board which includes the wiring required to interconnect the plurality of electromagnetic coils and to ground the stators of these coils. Each individual coil is fixedly secured and electrically connected to the annular circuit board. The circuit board includes foil for contacting each of the stators of the coils and circuitry to electrically connect the stators to the motor brake housing using a conductive stand off. In one embodiment, the stand off is integral with the motor brake housing. This assembled circuit board is then located relative to the stand off of the coil housing. Once provisions have been made for providing connection to an external power source, the assembly of the circuit board and the electromagnetic coils can be potted with the coil housing. The use of the printed circuit boards thus eliminates both the circumferential locating of the individual electromagnetic coils as well as the tedious task of wiring each individual electromagnetic coil. Each stator of the coils is electrically grounded and a plurality of holes extending through the circuit board permit the potting material to surround and establish the assembly. Thus, the assembly of the brake unit is simplified and the reliability is significantly improved.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.